Building a tube matcher

[jcr1234]

The DIY tube matcher described in Webers book is only able to test tubes like the 6v6, 6l6, el34 etc with the cathode on pin 8. If I want to build one to match el84's do I build the same rig but with the banana plugs and resistor on pin 3 since that is where the cathode is on the el84?

Has anybody ever done this?

Thanks,
Jon

[FYL]

I'd rather start with the PriceLess design: http://priceamp.home.comcast.net/~price ... atcher.htm

Just add noval sockets and their glue and you could test nearly all common power tubes.

[Structo]

Now that is pretty cool!

Thanks for that!

[jcr1234]

Thats very cool, but it is way more complicated and expensive than I need. Has anyone built the one in Weber's book? Would it work for el84's with the test point on pin 3?

[FYL]

What Weber describes in "Tube Amp Talk for the Guitarist and Tech" isn't a tube matcher but a simple bias probe. It should work for EL84's provided that you wire it properly.

[Phil_S]

Build yourself a modest fixed bias amp with a bias pot in it. It can be push pull or single ended. Amps make decent tube testers and they run the tubes at real loads and voltages. If you want to test big octals like EL34, 6L6, KT66. etc. use a universal type output transformer of adequate voltage rating. You can finess the load requirement by using the 4-8-16 ohm taps at either half or 2X depending on the tube. This can be done inexpensively if you find a used power transformer. One with multiple secondaries (or screen taps) might be useful to give you options for plate voltage.

[skyboltone]

Build yourself a modest fixed bias amp with a bias pot in it. It can be push pull or single ended. Amps make decent tube testers and they run the tubes at real loads and voltages. If you want to test big octals like EL34, 6L6, KT66. etc. use a universal type output transformer of adequate voltage rating. You can finess the load requirement by using the 4-8-16 ohm taps at either half or 2X depending on the tube. This can be done inexpensively if you find a used power transformer. One with multiple secondaries (or screen taps) might be useful to give you options for plate voltage.

As a matter of fact this is the recommended way to test output transformers too. Not at all difficult and you'll be happier with the result.

$.02 worth

[selloutrr]

keep in mind when testing tubes your results are only as good as the the voltage you are using to test.

when i was in the market for a tube tester i looked at probably 60 current production and a hundred vintage ones. the biggest problem was out of all of them only a dozen had voltages high enough to equal a tube amp.

if you test a tube at 250 volts. that does not mean that tube will behave the same at 300, 350, 400, 450, 500 volts.

If you only want to match output tubes. the best commercial stand alone tube tester/matcher is the Maxi Matcher offer up to 500volts.

If you just want to test a pair of tubes at home build a couple bias probs and hook them up to your amp and if the measuremetns are the same then the tubes are matched.

[Phil_S]

if you test a tube at 250 volts. that does not mean that tube will behave the same at 300, 350, 400, 450, 500 volts.

I think this is a really good point. Now, someone tell me if I've got the next point correct. One of the things to determine, especially for matching power tubes, which experience significant voltage swings under operating conditions, is transconductance (Gm). A transconductance match occurs when you have two tubes that will exhibit the same change in current draw as plate voltage changes.

(Note: not everyone gives the same weight to whether tube matching is important. That's not the topic of discussion. This is about "how to" not "whether to.")

To find transconductance involves getting several readings at different operating points and comparing the data. If you are doing this in an amp with a bias pot, you do it by changing the bias voltage. Maybe this isn't quite as nice as being able to vary the plate voltage, but math is math and you still get a valid calculation. I wonder, will the installation of a VVR give you what you need to properly vary plate voltage?

The formula for computing transconductance is relative and involves two measurement points that compare the change in plate current to the change in grid voltage. Wiki has a decent writeup: http://en.wikipedia.org/wiki/Transconductance look for the one-liner on vacuum tubes.

Take two measures and find the change in plate current. Divide that by the change in grid voltage. Multiply by 1000. That is Gm.

I've done a bit of this. I found it useful to get three readings and to calc Gm for the difference between 1 and 2, 2 and 3, and 1 and 3. This is a bit cumbersome if you've got lots of tubes. I guess you can't have too much data, though. If you are going for it, you really should go for it and not do half a job.

[selloutrr]

you can take it one step farther and do a curve trace. this will let you see exactly how the tube swings under voltage.

[Structo]

When I built my Dumbleator (tube buffered FX loop) which uses one 12AX7, I found it worked pretty good as a preamp tube tester.
It circuit has a plate loaded half and the other half is a cathode follower.

I had a bunch of Baldwin 12AX7 pulls and went through them and recorded the plate and cathode voltages and wrote that on some plain white tube boxes.
Now these numbers don't mean a thing to anybody but me but I can look at my stash and see at a glance which tubes are strong, medium or weak.

I would love to get one of those modern digital tube testers, those things are so cool!

[FYL]

I would love to get one of those modern digital tube testers, those things are so cool!

You may build one yourself using relatively cheap modules:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0551744281
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0526580974

[txbluesboy]

Thats interesting. Can someone translate?

[M Fowler]

Module lampemètre analyzer equipped with a microprocessor. Just connect a small 24 volt transformer ( 0.15A ) and a high voltage transformer and the heating lamps to achieve a
lampemètre functionally capable of testing all types of tubes , edit the families of curves and automatically get the characteristic values of slope ( Gm) , internal resistance ( Rp) and gain ( μ ) .

The device works with a computer ( via serial port or USB adapter) and all metrics are then programmed , or alone with a simple oscilloscope, the screen shots on the photos attached .

The software has been completed and the analyzer can work now in triode mode or "other "( lamps multigrid : tetrodes , penthodes , etc. ...). In the latter mode a voltage screen Annex will be supplied to the tube.

The card is supplied cable , set ready for use , along with its software pc cd (windows all versions from win95 to Vista included ) and the manual setup and use. The RS232 connector is also connected to the module .

Those which use this module already can contact me and I am happy to send them the new software so that they can enjoy all the possibilities.

Full documentation in english with detailed informations available on request.

Expédition France en Colissimo 6,40 euros.

Shipping cost to Europe: 14 euros including insurance.

Other countries please ask.

[Structo]

OK Mark beat me to that one.
The second one says:

This module lampemètre ultracompact operates under a low voltage and a power supply reduces. His performance makes possible the realization of a portable self lampemètre, powered by batteries or batteries, which did have nothing to envy the models of the most sophisticated laboratory. It is presented in a test situation with ECC82 - 12AU7 in the first photo.

Summary of Features:

Module dimensions: 100 mm x 125 mm max height + 25mm backlit LCD display 36 x 80 mm.

Single power supply: 5 or 6 V AC - AC (transformer), the recovery is already on the card, or 5.5 V to 9 V DC.

Consumption: 120 mA average, 150 mA (LCD lights included).

Power converter regulated high voltage, adjustable from 30 v to 300 volts minimum.

Gate bias generator adjustable from 0 to v - 32 volts minimum (resolution 0.1 volts).

Plate current range: 0-300 mA 2 subranges Automatic: 0 to 34.0 mA (0.1mA resolution) and 34-300 mA (resolution 1mA)

Note: These values are real, the use of a microprocessor allows high-speed measurement mode that minimizes the energy supply. Few traditional lampemètres are capable of such measures because they require heavy and bulky power supplies - the famous Metrix 310, for example, is limited to 100mA of plate current.

The operation of the device is very simple: Just set, by means of two potentiometers, the anode voltage and gate bias voltage to the desired values and, simultaneously, the plate current corresponding s' displays on the lcd screen. Measures' s conduct at the rate of 2 per second, which allows streaming of the 3 parameters. The second picture (LCD) sets out details of measurement of a new EL84 in triode mode: in the bottom left the plate voltage (280V), center the plate current (152 mA) for the value of the gate (-2.5 V), bottom right. These values are typical of those of the manufacturer. Here is a great site for tube characteristic: http://www.tubedata.org/

The test tubes or tetrodes penthodes effect by pseudo-triode mode which allows you to fully enjoy the linearity of these tubes (or g2 screen connected to plate), if the mode is true tetrode or penthode wanted it suffices to continuously applied to the screen / g2 voltage specified for the test, the bias voltage is controlled by the microprocessor and blocks the tube cut-off between the measures and n 'are, therefore, no risk of grid current .

The heating tubes can be withdrawn from the power supply module, a printed circuit area is prepared for a LM317 and its peripheral components that provide, possibly, a regulated voltage to the filament. For direct heating tubes a separate power supply must be provided.

The measurement accuracy is 5% and protections are integrated.

It is also possible to use the high voltage power supply module for testing circuits or small receivers. (Max speed of 28 mA at 80 V, 12 mA at 250 volts)

The module will be shipped wired, adjusted and ready for use with the display connected by a flexible sheet + the instruction manual, schematic diagram and details of connection and operation.

The plate that supports the test tube is not included in the auction but available on request with support Octal + support noval installed.

Documentation available on request with valid e-mail because the file is large and can not be sent by e-mail e-bay.